Structural Stress Analysis And Simulation On Casing-cement Ring In Oil And Gas Wells

The casing-cement sheath structure is a common combination structure in oil and gas wells,in which the cement sheath plays an important role in protecting and fixing the casing,sealing and isolating the oil and gas water layers.During the operation of oil and gas wells,the cement sheath in the composite structure will be damaged and lose its sealing and protective function,which will lead to damage to the casing and affect the safe operation of oil and gas wells.In order to further analyze the stress state of the casing-cement sheath structure in the event of failure,the basic mechanical performance parameters of the cement stone were obtained through uniaxial compression test,uniaxial tensile test and shear strength test in this paper.Based on elastic mechanics,the casing-cement sheath-stratum composite model was established by Abaqus software,and the Mises stress of each structural layer was simulated and analyzed when the composite body was subjected to non-uniform in-situ stress,and the changes of cement stone mechanical parameters and formation mechanical parameters were obtained.The influence law of Mises stress on the inner wall of the pipe,and the influence law of the Mises stress on the inner wall of the casing when the geometric size of the composite model changes and the absence of the cement sheath.The results obtained from the three basic mechanical properties experiments show that:the cement stone uniaxial compressive test sample does not have a yield stage before failure,the bearing capacity drops sharply after failure,the residual strength is basically zero,and the sample is extremely brittle;The elastic modulus of the stone is 5.96 GPa,and the Poisson’s ratio is 0.148;the stress-strain curve of the Brazilian splitting test of the cement stone sample changes in four stages,and the tensile strength of the cement stone is 2.04MPa;through the cement stone direct shear test The cohesion and internal friction angle of the cement stone are 13.58 MPa and33°.Using finite element software to analyze the Mises stress of the casing inner wall under different conditions,it is found that the stress of the casing inner wall is significantly higher than the stress of the cement sheath and the inner wall of the formation,and the distribution along the circumference of the well is uneven;The change has the greatest impact on the inner wall stress of the casing,followed by the elastic modulus of the cement stone and the elastic modulus of the formation,and finally the Poisson’s ratio of the cement sheath and the formation Poisson’s ratio.With the increase of the missing angle of the cement sheath in the composite structure,the area of Mises stress concentration on the inner wall of the casing gradually increases;the absence of the cement sheath on the first and second cemented surfaces will cause stress concentration,and the absence of the first cemented surface will affect the The protection of the casing is even more disadvantageous.The research results have certain theoretical guiding significance for optimizing oil and gas well design and avoiding casing damage.